The present invention relates to a process for producing finely particulate calcium silicates by modifying smectites and the like, as well as calcium silicates excellent in whiteness, cation exchange capacity, and adsorbability, which are obtained by the production process.
Further, the present invention concerns an antibacterial calcium silicate, in which an antibacterial metal is carried on calcium silicates.
Antibacterial agent in admixture with a synthetic resin or the like, used for preventing miscellaneous bacteria from proliferating, include organic nitrogen series antibacterial agents and inorganic antibacterial agents having antibacterial metals carried on inorganic powder. Existent organic nitrogen series antibacterial agents have an excessively strong antibacterial effect, and they therefore involve the problem of having undesired effects on the human body or the natural environment. On the other hand, the use of safe antibacterial agents not having an excessively strong antibacterial effect involves the problem that the antibacterial effect is insufficient, unless the concentration of the antibacterial agent is controlled to a sufficiently high level near the surface of synthetic resin products and the like.
It has been known that metals, such as silver or copper or ions thereof, have sterilizing and antibacterial effects, and such metal ions, metal particles, or metal compounds are carried on inorganic materials and are released gradually therefrom, to provide antibacterial ability in inorganic antibacterial agents. As the carrier for the inorganic antibacterial agents, zeolite, apatite, phosphate, clay mineral, and glass are used. Since the carriers are inorganic materials, they can be said to be excellent in view of durability and heat resistance, and to be safe, having less effects on the human body or the like, compared with existent organic antibacterial agents.
In the meantime, among the antibacterial metals used in existent inorganic antibacterial agents, silver exhibits antibacterial ability to variety of bacteria, and it has strong antibacterial power. But silver has a drawback of low solubility. Further, antibacterial agents using silver cause coloring, and the application use is limited in the case of blending into synthetic resin, paint, or rubber by kneading or mixing. Further, silver ions cannot be supplied in an amount sufficient to suppress bacteria deposited on the surface of products, and, as a result, it has been difficult to provide sufficient antibacterial strength.
Specifically, it has been proposed to produce sterilizing silicates, from layerous silicates, such as smectites by replacing its cation with silver, copper, or the like, by utilizing their cationic exchanger ability as they are (JP-A Nos. Hei 2-19308 and Hei 3-193707), but they cannot be said to be sufficient in view of the sterilizing ability and the whiteness while the purified layerous silicates are used.
Further, existent natural calcium silicates are being deteriorated in cation exchange ability and adsorbability, and antibacterial agent-retaining ability, along with efflorescence. Therefore, such clay minerals wethered have little worth in practical use, and they are not suitable to various application uses for clay minerals that have crystalline structure.
It is, accordingly, an object of the present invention to provide calcium silicates excellent in the performances described above and easy to give a form of particulates that can be produced by utilizing by regenerating clay minerals which are deteriorated in the cation exchange ability and the adsorbability along with efflorescence, as well as a production process therefor.
A further object of the present invention is to provide an antibacterial silicate (antibacterial material) which is safe, having good whiteness and retaining of ability of antibacterial agent and capable of exhibiting a sufficient antibacterial power when used in synthetic resin, paint or rubber.
A further object of the present invention is to provide a process capable of producing, at low cost, inorganic antibacterial material which can be used for various application uses and have sufficient antibacterial power.